The present invention relates to a disposable device for centrifugation of blood, which is used to separate or also wash constituents of the blood. Such blood can be whole blood, for example, or blood from which the leukocytes have already been removed by filtration, or blood flowing from an operating site.
Centrifugation is the most commonly used technique for separating blood constituents, such as red blood cells, plasma, white blood cells and platelets, from blood originating directly from the donor, from a collection bag, from an operating site or from a blood sample. This is done using separators that are composed of a centrifugation chamber driven in rotation about a vertical shaft by a motor capable of turning at high speed, generally between 1,000 and 50,000 rpm. The blood is introduced continuously or non-continuously into the centrifugation chamber by way of an inlet channel that forms part of a fixed axial member of the centrifugation device.
Under the effect of the centrifugal force, the various constituents of the blood separate on account of their different densities. This separation takes place naturally in a predefined order, such that the blood constituent of greater density, namely the red blood cells, is always positioned at the greatest possible distance from the axis of revolution, whereas the constituent of lower density will always be situated nearer this axis than all the other constituents. By means of this separation in distinct layers, these constituents can be extracted separately by collectors that extend respectively into the stratification zones. In this way, each blood constituent is conveyed separately to an outlet channel situated in the fixed axial member of the device. Once they have been extracted from the centrifugation chamber via these outlet channels, they can be collected in separate bags or re-injected into the patient.
Such a device is described in more detail in patent application EP 05405037. When it is intended to be used in non-sterile environments, for example in blood transfusion centers or in a hospital environment, it is imperative to be able to guarantee the sterility of all the volumes through which the blood and its constituents will pass. To meet this requirement, the separation kits are made ready in a sterile package and are designed in such a way as to define a closed space that is hermetically sealed off to entry of any gas or fluid other than blood. To this end, the various bags for collecting the blood products are generally pre-connected to the separation kit.
The sterility of this assembly would not be complete unless a means was provided to ensure non-contamination of the centrifugation chamber at the place where the fixed and movable parts join, namely between the axial member for admission/evacuation and the centrifugation chamber. This means must satisfy two main criteria, namely that of guaranteeing the sterility of the centrifugation device, and also that of permitting high speeds of rotation of the centrifugation chamber while minimizing the heating between the fixed and movable parts of the device. This latter criterion is aimed at preventing heating of the blood by conduction within this device. The reason is that it is imperative to keep the blood at a temperature below 40° C. in order to avoid degradation of its constituents.
In an attempt to satisfy these criteria, various systems have been used, of which one example is the device described in document U.S. Pat. No. 3,586,413 and known to a person skilled in the art by the term “lasso”. This system involves the provision of a flexible tube, of which one end is integrally connected to the center of the centrifugation chamber, and of which the other end is integrally connected to a fixed part of the device. The two ends of this tube give it the shape of a half loop that is rotated about the centrifugation chamber at a speed equal to half that of the chamber. This system allows a connection to be created between the tube and the centrifugation chamber without friction and without any heating other than that arising from the bending and twisting forces of the flexible tube as it rotates about itself. The main disadvantages of this device are that it is of complex construction, it involves awkward rotation of a tube about the centrifugation chamber, and this tube is subjected to a substantial tensile stress generated by the centrifugal force to which it is subjected.
Document U.S. Pat. No. 5,045,048 describes another device, which is much simpler to produce than the preceding one, and in which the junction between the fixed admission/evacuation conduits and the rotatable chamber is formed by a pair of components that between them have a very low coefficient of friction. The first component forms part of the fixed kit and, in order to guarantee the leaktightness of the connection, it bears against the second component, which is integrally connected to the centrifugation chamber. This coupling of the components can be effected by means of a V-ring made of polymer, turning on a metal washer, or can be formed by a ceramic ring bearing on a graphite ring. Although this system has the advantages of low production costs and of being simple to use, it nevertheless has the disadvantage of limiting the maximum speed of rotation of the chamber, because of the heating induced in the components rubbing against each other.
In order to reduce this heating, consideration has also been given to the idea of adding a plurality of ventilation fins arranged near the surface of friction of the two components rubbing against each other. The provision of such a ventilated joint inside a centrifugation device does indeed contribute to improving the dissipation of heat emanating from these components, but without being entirely satisfactory. Such a device is described in more detail in document EP 619,145.
In patent application EP 05,405,037, the leaktightness between the fixed and movable parts of the centrifugation device is effected by means of a tubular joint. One of the ends of this joint is fixed on a cylindrical portion of the fixed axial member, while the other end is introduced into an annular space of the neck of the centrifugation chamber, bearing against a convex surface of this neck. By virtue of this bearing, the tubular joint undergoes radial deformation which ensures the leaktightness of the centrifugation chamber. Although the diameter of the neck of the centrifugation chamber against which this joint rubs is a small diameter, the fact remains that heating is caused directly as a function of the speed of rotation of the chamber. With this system, the maximum speed of rotation is limited because of this heating. In addition, using chambers provided with a neck of greater diameter would again render unsatisfactory the use of this tubular joint for solving said problem of heating.